sleep calculator
Find the best time to wake up or go to bed — based on 90-minute sleep cycles — wake up refreshed every morning.
Sleep cycle duration varies between individuals. These times are based on the average 90-minute cycle. Results are a guide — not medical advice. Consult a doctor for sleep disorders or chronic fatigue.
Sleep by age group
| Teen (14–17) | 8–10 hrs |
| Adult (18–64) | 7–9 hrs |
| Older (65+) | 7–8 hrs |
| 1 cycle | 90 minutes |
| 5 cycles | 7.5 hours ✅ ideal |
| 6 cycles | 9 hours ✅ ideal |
What is a sleep cycle?
Each sleep cycle lasts about 90 minutes and moves through light sleep, deep sleep, and REM (rapid eye movement) sleep. Your brain consolidates memories and repairs the body during deep sleep, while REM drives creativity and emotional processing.
Why do I wake up groggy?
Grogginess — called sleep inertia — happens when your alarm goes off mid-cycle during deep sleep. Waking at the natural end of a cycle means your brain is already transitioning to light sleep, so you feel alert immediately.
FAQ
Is 6 hours of sleep enough?
For most adults, no. Six hours equals 4 sleep cycles — below the recommended 5 to 6. Chronic short sleep is linked to increased health risks. Aim for at least 7.5 hours (5 cycles).
What if I fall asleep faster or slower?
Adjust the "time to fall asleep" setting. The average is 14 minutes. If you tend to fall asleep quickly, select 5–10 minutes. If it takes you longer, select 20–30 minutes.
Does napping help?
A 20-minute nap avoids deep sleep and prevents grogginess. A 90-minute nap completes one full cycle. Avoid napping after 3 PM as it can affect night-time sleep.
Is my data stored?
No — everything runs in your browser. No data is ever uploaded or stored.